DOCSLIB.ORG

The Rift-Related Mafic Dyke Complex of the Rohkunborri Nappe, Indre Troms, Northern Norwegian Caledonides

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Rift-Related Mafic Dyke Complex of the Rohkunborri Nappe, Indre Troms, Northern Norwegian Caledonides The rift-related mafic dyke complex of the Rohkunborri Nappe, Indre Troms, northern Norwegian Caledonides LARS KRISTIAN STØLEN Stølen, L. K.: The rift-related mafic dyke complex of the Rohkunborri Nappe, Indre Troms, northern Norwegian Caledonides. Norsk Geologisk Tidsskrift, Vol. 74, pp. 35-47. Oslo 1994. ISSN 0029-196X. Well-preserved dyke complexes are found within the Seve Nappe Complex, Upper Allochthon, in the easternmost part of Indre Troms, Norway. They form a separate thrust sheet, the Rohkunborri Nappe, and are best exposed in two low-strain units in the Rohkunborri and Njunis areas. In these areas the dolerite swarm intrudes a succession of carbonate rocks and subordinate sandstones, siltstones and quartzites. The sedimentary rocks, the Nj unis Group, are supposed to represent the outermost part of the clastic wedge deposited during Neoproterozoic-earliest Palaeozoic time on the thinned outermost part of the Baltoscandian margin. A complex structural evolution can be recognized within the dyke complexes involving early block rotation d.uring intrusion, rotation of both dykes and bedding due to simple shear deformation during thrusting and subsequent imbrication of the dyke complex. The Indre Troms dykes are part of the Neoproterozoic- Early Palaeozoic rifted Baltoscandian margin and represent the transition zone between the continent Baltica and the Iapetus ocean. The Rohkunborri Nappe can be correlated with the Vaivvancohkka Nappe and the Sarektjåkkå Nappe of the Seve Nappe Complex in the northemmost Swedish Caledonides. Lars Kristian Stølen, Department of Mineralogy and Petrology, Institute of Geo/ogy, University of Lund, Solvegatan 13, S-223 62 Lund, Sweden. Introduction the latest Proterozoic to Early Cambrian passive margin of baltica (Gee 1975; Andreasson 1987). Mafic dyke swarms are known from several parts of the The tectonic units of the Koli Nappe Complex that Scandinavian Caledonides. They occur in the autochthon overlie the Seve units locally are composed of a variety of and lower thrust sheets in the northernmost parts of the . terranes derived from outboard of Baltica (Stephens & mountain belt; further south, they occur only in the Gee 1989). At least two episodes of mafic igneous activ­ allochthons. According to a terminology introduced by ity related to the development of ophiolites and are Kulling ( 1972) and Gee & Zachrisson (1979), the al­ spreading are recorded within the Koli Nappe Complex. lochthons can be divided into four major tectonostrati­ One is of Early Ordovician age and represented by the graphic units: Lower, Middle, Upper and Uppermost. The Lower Allochthon is dominated by Vendian and Karmøy and Leka ophiolite complexes (Furnes et al. Lower Palaeozoic successions, the Middle Allochthon by 1988 ; Pedersen et al. 1988 ; Pedersen & Hertogen 1990) ; thick Vendian and Upper Proterozoic strata, together the other is Late Ordovician to earliest Silurian in age with sheets of Precambrian crystalline rocks. The succes­ and represented by the Solund/Stavfjorden ophio1ite sions of the Lower Allochthon are readily correlated with (Furnes et al. 1980; Dunning and Pedersen 1988). Mafic those of the Baltoscandian Platform Autochthon; those complexes imruded during rifting of volcanic arcs and in the Middle Allochthon are supposed to have been fo rmation of marginal basins in the northern Scandina­ derived fr om the Baltoscandian miogeocline. vian Caledonides, e.g. the Sulitjelma lgneous Complex The uppermost tectonic units of the Middle Al­ (Pedersen et al. 1991) and the Råna Massif (Tucker et al. lochthon (Sarv Nappe) were thrust fr om the outer part 1990), have a similar age to the Solund/Stavfjorden of the Baltoscandian miogeocline; they are extensively ophiolite. intruded by mafic dyke swarms (Stromberg 1969) related As part of a more comprehensive study of the relation­ to Late Proterozoic rifting (Gee 1975; Solyom et al. ships between inboard and outboard terranes in northern 1979; Claesson & Roddick 1983), which extended more parts of the Scandinavian Caledonides, this study deals than l 000 km along the Baltoscandian margin (Andreas­ with mafic dyke swarms occurring in the easternmost son 1987). parts of Indre Troms, and fo cuses on their made of The lower part of the overlying Upper Allochthon, occurrence and tectonostratigraphic position. Previous composed of the Seve Nappe Complex, is an imbricate work, e.g. Gee et al. ( 1985a, b) , has inferred a late stack of lithotectonic units (Andreasson 1986) character­ Proterozoic age for the dykes and has correlated these ized by tholeiitic metabasites (locally as dyke swarms) units with those occurring in the Seve Nappe Complex in and psammitic schists. lts complexes are also inferred to northern Sweden. The evidence presented here supports be indigenous, and derived from the outermost part of this hypothesis. 36 L. K. Stølen NORSK GEOLOGISK TIDSSKRIFT 74 (1994) The Baltoscandian margin nized in Sweden as far north as central Norrbotten (Fig. I). The more complexly deformed a�d highly �etamor­ In the central part of the Scandinavian Caledonides (Fig. phosed Seve Nappe Complex, overlymg the Mtddle Al­ I) evidence from the Lower and Middle Allochthons lochthon in Sweden, contains a similar, but somewhat provides constraints on the evolution of the Bal�oscan­ more complex protolith, including both volcano-sedi­ dian margin. Stratigraphic correlations (Kumpulamen & mentary Baltoscandian miogeoclinical succes�ions (A�­ Nystuen 1985) of Late Proterozoic to Lower Cambrian dn!asson 1987) and elements of the Proterozotc cratomc sedimentary rocks within these thrust sheets have estab­ margin. lished three informal units: a thick lower mainly fluviatile The lower part of the Seve Nappe Complex in Nor­ unit, a middle glacial unit (Varangian) and an upper rbotten, the Vaimok Lens (Fig. 2), contains a dolerite-in­ fluviatile and shallow marine unit of Late Vendian to truded metasedimentary sequence, with similarities to the Early Cambrian age. In northem areas, the upper unit underlying Sarv Nappe, but metamorphosed to ec��git: dominates the autochthon and the middle unit is also grade. These units are overthrust by the Sarektjakka locally preserved; further south all three units are gener­ Nappe (Svenningsen 1987), which is dominated by Ven­ ally allochthonous and the autochthonous strata · are dian mafic dykes (8 0%), occurring as sheeted complexes, mainly Mid-Cambrian to Ordovician. The Vendian and with screens of quartzites, meta-arkoses and subordinate Late Proterozoic successions can be readily correlated carbonates, showing similarities with the Tossåsfjellet with sequences within the Middle Allochthon at !east as Group of the Sarv Nappes (Kumpulainen 1980). far north as the Akkajaure area (Kumpulainen & Further north, in the Kebnekaise area, the nearly Nystuen 1985). l 00 % dyke-dominated Kebne dyke complex (Andreas­ Stratigraphical and sedimentological studies (Kumpu­ son & Gee 1989) can be correlated with the Sarektjåkkå lainen 1980; Kumpulainen & Nystuen 1985) indicate that Nappe. Near the Norwegian border in the Tometrask the pre-Vendian successions were deposited in rift-related area, Kathol ( 1989) mapped a sequence of dyke-intruded basins along the Baltoscandian margin. The extensive sandstones with cross- and graded-bedding in the Vaiv­ Late Proterozoic tholeiitic dyke swarms of the Sarv vancohkka Nappe, overlying augen gneisses with eclogi­ Nappe suggest several tens of kilometres of passive mar­ tized metabasite lenses. He included all these units in the gin extension. These dyke complexes have been recog- Seve Nappe Complex. The high-grade Seve augen gneisses, together with units from the underlying Middle Allochthon, can be followed northwards from Tome­ trask ' via the area of Indre Troms, treated in more detail here, to Treriksrøysa (Stølen 1989), where the Seve units pro bably wedge out (e.f. Zachrisson 1986). ' -­ _ _ , In northem Norway, mafic dyke swarms occur in units ' correlated (Gee et al. l985a, b) with the upper part of , , Middle Allochthon and the overlying Vaddas (Koli) Map area fig. 3 Nappe. In the upper Middle Allochthon, the dyke-in­ truded units are closely comparable with those in the Sarv Nappe (and Seve in Norrbotten) and have been correlated with them (e.g. the Corrovarre Nappe of 1100 km l Zwaan & van Roermund 1990). In the Vaddas Nappe the mafic rocks occur both as dykes and as basalts in a LEGEND : � Late Ordovician succession. Thus, in this part of the N Uppermost Allochthon mountain belt, dyke complexes that were injected in the Vendian and in the Ordovician are juxtaposed. D UpperAllochthon : \ b:::l KOii Nappe Complex The Corrovarre dykes have been dated to c. 580 Ma (Zwaan & van Roermund 1990) and correlated with • Upper Allochthon : Seve Nappe Complex those in the Seiland Igneous Province. The latter are thought to have formed during thinning and rifting of R Lower and Middle l::1::jAllochthon the Baltoscandian shield prior to Finnmarkian deforma­ tion (Roberts 1990; Zwaan & van Roermund 1990). • Autochthonous sediments The Vaddas Nappe contains fossiliferous rocks of Late Ordovician or Early Silurian age (Binns & Gayer 1980) r-::::1 Para·autochthonous t;;:Jcrystal line basement and Late Ordovician basalts. The lower part of the rocks in windows Vaddas Nappe is composed of interlayered marb1es and schist overlain by a quartzite-dominated unit (Padget Fig. 1. Simplifiedtectonostratigraphic map of the northem part of the Scandina­ 1955). These units are overlain by a sequence of fossili­ vian Caledonides.
Load more

Recommended publications
  • Strike and Dip Refer to the Orientation Or Attitude of a Geologic Feature. The
    Name__________________________________ 89.325 – Geology for Engineers Faults, Folds, Outcrop Patterns and Geologic Maps I. Properties of Earth Materials When rocks are subjected to differential stress the resulting build-up in strain can cause deformation. Depending on the material properties the result can either be elastic deformation which can ultimately lead to the breaking of the rock material (faults) or ductile deformation which can lead to the development of folds. In this exercise we will look at the various types of deformation and how geologists use geologic maps to understand this deformation. II. Strike and Dip Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature, is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented parallel to the strike line. Strike (or strike angle) can be given as either a quadrant compass bearing of the strike line (N25°E for example) or in terms of east or west of true north or south, a single three digit number representing the azimuth, where the lower number is usually given (where the example of N25°E would simply be 025), or the azimuth number followed by the degree sign (example of N25°E would be 025°). The dip gives the steepest angle of descent of a tilted bed or feature relative to a horizontal plane, and is given by the number (0°-90°) as well as a letter (N, S, E, W) with rough direction in which the bed is dipping.
    [Show full text]
  • GEOL360 Structural Geology Problem Set #3: Apparent Dip, Angles And
    GEOL360 Structural Geology Name______________________ Date_______________________ Problem Set #3: Apparent Dip, Angles and Orientations Part 1. Apparent dip 1. In a mine, a tabular dike has an apparent dip of 14°, 270° in one tunnel and 25°, 169° in another tunnel (here we use azimuth directions). Using a stereonet, what is the attitude (strike and dip) of the dike? _____________________ 1. Along a vertical railroad cut a bed has an apparent dip of 20°, N62°W. The bed strikes N67°E. What is the true dip? _____________________ 1. Suppose a fault strikes N10°E and its apparent dip trends S26°E and plunges 35°. Using a stereonet, determine the true dip of the fault. _____________________ Part II. Angle between two lines 1. What is the angle between the following two lines? a. 35°, S10°E a. 15°, N23°W _____________________ 1. What is the angle between the following two lines? a. 12°, N8°E a. 40°, S19°W _____________________ 1. What is the angle between the following two lines? a. 70°, S38°E a. 49°, N15°E _____________________ Part III. Angle between two planes 1. What is the angle between the following two planes? a. N27°E, 85°SE a. N89°W, 7°NE _____________________ 2. What is the angle between the following two planes? a. 315°, 20°NE a. 165°, 24°SW _____________________ 3. What is the angle between the following two planes? a. 014°, 10°SE a. N18°W, 37°NE _____________________ Part IV. Orientation of the intersection of two planes: 1. Determine the orientation of the intersection of the following two planes: a.
    [Show full text]
  • Dike Orientations, Faultblock Rotations, and the Construction of Slow
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL 103, NO. B1, PAGES 663-676, JANUARY 10, 1998 Dike orientations, fault-block rotations, and the constructionof slow spreading oceaniccrust at 22 ø40'N on the Mid-Atlantic Ridge R6isfn M. Lawrence and Jeffrey A. Karson Divisionof Earthand Ocean Sciences, Duke University,Durham, North Carolina StephenD. Hurst DepartmentofGeology, The University ofIllinois, Urbana, Illinois Abstract. The firstpalcomagnetic results from oriented dike samples collected on the Mid- AtlanticRidge shed new light on thecomplex interplay between magmatic accretion and mechanicalextension at a slowspreading ridge segment. An uppercrustal section about 1.5 km thickis exposed along a west-dippingnormal fault zone that defines the eastern median valley wall of thesouthern segment of theMid-Atlantic Ridge south of theKane fracture zone (MARK area). Twodistinct groups of dikesare differentiated onthe basis of orientationand palcomagnetic characteristics.One group, on the basis of thepalcomagnetic data, appears to bein itsoriginal intrusionorientation. This group includes both ridge-parallel, vertical dikes as well as dikes in otherorientations, calling into question assumptions about uniform dike orientations at oceanic spreadingcenters. The second group consists ofdikes that have palcomagnetic directions that are distinctfrom the predicted dipole direction, and we interpret them to have been tectonically rotated. Thesealso occur in manyorientations. The spatial relations between rotated and nonrotated dikes indicatethat intrusion, faulting, and block rotation were contemporaneous beneath the median valleyfloor. Nonrotated dikes exposed onthe eastern median valley wall indicate that there has beenno net rotation of thisupper crustal assemblage since magmatic construction ceased. Hence slipand associated uplift probably occurred inthe fault zones' present orientation. These results providethe basis for a generalmodel of mechanical extension anddike intrusion forthis segment ofthe Mid-Atlantic Ridge.
    [Show full text]
  • Magma Genesis and Arc Evolution at the Indochina Terrane Subduction
    feart-08-00271 July 13, 2020 Time: 10:29 # 1 ORIGINAL RESEARCH published: 14 July 2020 doi: 10.3389/feart.2020.00271 Magma Genesis and Arc Evolution at the Indochina Terrane Subduction: Petrological and Geochemical Constraints From the Volcanic Rocks in Wang Nam Khiao Area, Nakhon Ratchasima, Thailand Vanachawan Hunyek, Chakkaphan Sutthirat and Alongkot Fanka* Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok, Thailand Volcanic rocks and associated dikes have been exposed in Wang Nam Khiao area, Nakhon Ratchasima Province, northeastern Thailand where complex tectonic setting was reported. These volcanic rocks are classified as rhyolite, dacite, and andesite whereas dikes are also characterized by andesitic composition. These dikes clearly Edited by: cut into the volcanic rocks and Late Permian hornblende granite in the adjacent area. Basilios Tsikouras, Universiti Brunei Darussalam, Brunei Rhyolite and dacite are composed of abundant plagioclase and quartz whereas andesite Reviewed by: and andesitic dike contain mainly plagioclase and hornblende with minor quartz. The Toshiaki Tsunogae, volcanic rocks typically show plagioclase and hornblende phenocrysts embedded in University of Tsukuba, Japan fine-grained quartz and glass groundmass whereas dike rocks contain less glass matrix Gianluca Vignaroli, University of Bologna, Italy with more albitic laths. P–T conditions of crystallization are estimated, on the basis of Al- *Correspondence: in-hornblende geobarometry and hornblende geothermometry, at about 4.5–5.5 kbar, Alongkot Fanka 861–927◦C and 4.8–5.5 kbar, 873–890◦C for the magma intrusions that fed volcanic [email protected]; [email protected] rocks and andesitic dikes, respectively. Whole-rock geochemistry indicates that these rock suites are related to calc-alkaline hydrous magma.
    [Show full text]
  • Collapse Features and Narrow Grabens on Mars and Venus: Dike Emplacement and Deflation of Underlying Magma Chamber
    Lunar and Planetary Science XXXI 1854.pdf COLLAPSE FEATURES AND NARROW GRABENS ON MARS AND VENUS: DIKE EMPLACEMENT AND DEFLATION OF UNDERLYING MAGMA CHAMBER. D. Mege1, Y. Lagabrielle2, E. Garel3, M.-H. Cormier4 and A. C. Cook5, 1Laboratoire de Tectonique, ESA 7072, Universite Pierre et Marie Curie, case 129, 75252 Paris cedex 05, France, e-mail: [email protected], 2Institut de Recherche pour le Developpement, Geosciences, BPA5, Noumea, New Caledonia, e-mail: [email protected], 3Institut Europeen de la Mer, UMR 6538, Universite de Bretagne Occidentale, Place Nicolas Copernic, 29280 Plouzane, France, e-mail: [email protected], 4Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, e-mail: [email protected], 5Center for Earth and Planetary Studies, National Air and Space Museum, Washington, D. C. 20560, e-mail: [email protected] Summary: Grabens in the Tharsis region of Mars interpretation. However, the mechanism of deflation for a displaying aligned pit craters, and elongated troughs, cannot single event, resulting in a single collapse event, does not be explained by regional tectonic extension only. Similar necessarily imply spreading, and therefore may be compared grabens and troughs are observed at the summit of fast to a collapse event at a Martian graben. Crustal and lithosphere spreading ridges, such as the East Pacific Rise (EPR), where rheology used in experiment models must merely be adapted bathymetric and seismic data, as well as experimental to the Martian rheological conditions. Below we describe the modelling, suggest that they result from deflation and rheological conditions that we find the most likely, report compaction of an elongated magma body underneath.
    [Show full text]
  • University of Nevada Reno Dike Emplacement and Deformation In
    M’ MES Lf&SARY 3201 University of Nevada Reno Dike Emplacement and Deformation in the Donner Summit Pluton, Central Sierra Nevada, California Ch vS> C* This thesis is submitted in partial fulfillment of the requirements for the degree of Master of Science in Geological Engineering. by Kathleen Andrea Ward Dr. Richard Schultz/ Thesis Advisor December 1993 H ACKNOWLEDGEMENTS <Whew> I bet some of you out there figured I would never get done. But here I am with a completed M.S. thesis in geological engineering. I am not even sure where to begin and who to thank first, because each and every one of the following people have contributed so much to my life and my thesis. My mom and dad and Erika and Christy have always been supportive about my schoolwork. Without them close by in Sacramento with a guest room I would have gone crazy. I love them more than they can ever imagine. And no one will ever find a better field assistant than my sister Erika. Christina and Robert - What an incredible pair! Always had an extra room for me too, even in Florida. My grandma, who put up with me no matter what my mood. I love you. My e-mail account was priceless. The constant cheer and love I received from Becky, Kevin, and Erika helped me through many stressful times. The other graduate students who enjoyed the M.S. thesis ride with me, I salute each and every one of you. Especially Paul and Li (the two hardest workers in the department). Reno Mountain Sports, the entire crew, have been my constant sanctuary always making me take time out to smell the roses, or ski the powder...
    [Show full text]
  • Evaluation of Major Dike- Impounded Ground-Water Reservoirs, Island of Oahu
    Evaluation of Major Dike- Impounded Ground-Water Reservoirs, Island of Oahu By K. J. TAKASAKI and J. F. MINK With a Section on Flow Hydraulics in Dike Tunnels in Hawaii Prepared in cooperation with the Board of Water Supply City and County of Honolulu U.S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER 2217 DEPARTMENT OF THE INTERIOR DONALD PAUL MODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director UNITED STATES GOVERNMENT PRINTING OFFICE: 1985 For sale by the Distribution Branch, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 Library of Congress Cataloging in Publication Data Takasaki,K.J.(KiyoshiJ.) Evaluation of major dike-impounded ground-water reser­ voirs, Island of Oahu. (U.S. Geological Survey water-supply paper; 2217) Bibliography: p. Supt.ofDocs.no.: 119.13:2217 1. Water, Underground Hawaii Oahu. 2 Dikes (Geol­ ogy) Hawaii Oahu. I. Mink, John F. (John Fran- cis),1924- . II. Honolulu (Hawaii). Board of Water Supply. III. Title. IV. Series. GB1025.H3T34 1984 551.49'0969'3 83-600367 CONTENTS Abstract 1 Introduction 1 Purpose and scope 2 Evolution of the concept for the development of dike-impounded water Geologic sketch 4 Volcanic activity 4 Rift-zone structures 4 Marginal dike zone defined 6 Attitude of dikes 7 Dikes and their effects on storage and movement of ground water 7 Geologic framework of dike-impounded reservoirs 7 Factors controlling recharge and discharge of dike-impounded water 9 Dikes in the Koolau Range 11 Rift zones 11 Data base 11 Attitude and density of dikes 11 Strike or trend 11 Dip
    [Show full text]
  • GEOLOGIC MAP of the CHELAN 30-MINUTE by 60-MINUTE QUADRANGLE, WASHINGTON by R
    DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP I-1661 U.S. GEOLOGICAL SURVEY GEOLOGIC MAP OF THE CHELAN 30-MINUTE BY 60-MINUTE QUADRANGLE, WASHINGTON By R. W. Tabor, V. A. Frizzell, Jr., J. T. Whetten, R. B. Waitt, D. A. Swanson, G. R. Byerly, D. B. Booth, M. J. Hetherington, and R. E. Zartman INTRODUCTION Bedrock of the Chelan 1:100,000 quadrangle displays a long and varied geologic history (fig. 1). Pioneer geologic work in the quadrangle began with Bailey Willis (1887, 1903) and I. C. Russell (1893, 1900). A. C. Waters (1930, 1932, 1938) made the first definitive geologic studies in the area (fig. 2). He mapped and described the metamorphic rocks and the lavas of the Columbia River Basalt Group in the vicinity of Chelan as well as the arkoses within the Chiwaukum graben (fig. 1). B. M. Page (1939a, b) detailed much of the structure and petrology of the metamorphic and igneous rocks in the Chiwaukum Mountains, further described the arkoses, and, for the first time, defined the alpine glacial stages in the area. C. L. Willis (1950, 1953) was the first to recognize the Chiwaukum graben, one of the more significant structural features of the region. The pre-Tertiary schists and gneisses are continuous with rocks to the north included in the Skagit Metamorphic Suite of Misch (1966, p. 102-103). Peter Misch and his students established a framework of North Cascade metamorphic geology which underlies much of our construct, especially in the western part of the quadrangle. Our work began in 1975 and was essentially completed in 1980.
    [Show full text]
  • 4. Deep-Tow Observations at the East Pacific Rise, 8°45N, and Some Interpretations
    4. DEEP-TOW OBSERVATIONS AT THE EAST PACIFIC RISE, 8°45N, AND SOME INTERPRETATIONS Peter Lonsdale and F. N. Spiess, University of California, San Diego, Marine Physical Laboratory, Scripps Institution of Oceanography, La Jolla, California ABSTRACT A near-bottom survey of a 24-km length of the East Pacific Rise (EPR) crest near the Leg 54 drill sites has established that the axial ridge is a 12- to 15-km-wide lava plateau, bounded by steep 300-meter-high slopes that in places are large outward-facing fault scarps. The plateau is bisected asymmetrically by a 1- to 2-km-wide crestal rift zone, with summit grabens, pillow walls, and axial peaks, which is the locus of dike injection and fissure eruption. About 900 sets of bottom photos of this rift zone and adjacent parts of the plateau show that the upper oceanic crust is composed of several dif- ferent types of pillow and sheet lava. Sheet lava is more abundant at this rise crest than on slow-spreading ridges or on some other fast- spreading rises. Beyond 2 km from the axis, most of the plateau has a patchy veneer of sediment, and its surface is increasingly broken by extensional faults and fissures. At the plateau's margins, secondary volcanism builds subcircular peaks and partly buries the fault scarps formed on the plateau and at its boundaries. Another deep-tow survey of a patch of young abyssal hills 20 to 30 km east of the spreading axis mapped a highly lineated terrain of inactive horsts and grabens. They were created by extension on inward- and outward- facing normal faults, in a zone 12 to 20 km from the axis.
    [Show full text]
  • Field-Trip Guide to the Vents, Dikes, Stratigraphy, and Structure of the Columbia River Basalt Group, Eastern Oregon and Southeastern Washington
    Field-Trip Guide to the Vents, Dikes, Stratigraphy, and Structure of the Columbia River Basalt Group, Eastern Oregon and Southeastern Washington Scientific Investigations Report 2017–5022–N U.S. Department of the Interior U.S. Geological Survey Cover. Palouse Falls, Washington. The Palouse River originates in Idaho and flows westward before it enters the Snake River near Lyons Ferry, Washington. About 10 kilometers north of this confluence, the river has eroded through the Wanapum Basalt and upper portion of the Grande Ronde Basalt to produce Palouse Falls, where the river drops 60 meters (198 feet) into the plunge pool below. The river’s course was created during the cataclysmic Missoula floods of the Pleistocene as ice dams along the Clark Fork River in Idaho periodically broke and reformed. These events released water from Glacial Lake Missoula, with the resulting floods into Washington creating the Channeled Scablands and Glacial Lake Lewis. Palouse Falls was created by headward erosion of these floodwaters as they spilled over the basalt into the Snake River. After the last of the floodwaters receded, the Palouse River began to follow the scabland channel it resides in today. Photograph by Stephen P. Reidel. Field-Trip Guide to the Vents, Dikes, Stratigraphy, and Structure of the Columbia River Basalt Group, Eastern Oregon and Southeastern Washington By Victor E. Camp, Stephen P. Reidel, Martin E. Ross, Richard J. Brown, and Stephen Self Scientific Investigations Report 2017–5022–N U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior RYAN K. ZINKE, Secretary U.S.
    [Show full text]
  • 19840012886.Pdf
    42 STRUCTURAL VARIATION OF PROTEROZOIC DIKES IN THE CENTRAL SUPERIOR PROVINCE- A POSSIBLE REFLECTION OF POST-ARCHEAN SHIELD DEFORMATION, R. E. ERNST and H. C. HALLS, Dept. of Geology, University of Toronto, Toronto, Canada, M5S 1A1 Introduct i on Geodynamic modelling of shield areas requires a 3-D understanding of the geology. In lieu of deep drilling and geophysical work, the third dimension is revealed wherever the crust is tilted to expose a vertical section at surface. However, the identification of surface exposure with changing structural depth is generally difficult in shield areas owing to their typically complex deformation. In areas where the structural and metamorphic patterns provide inconclusive results, data from post-orogenic diabase dike swarms may prove usefuI. Undeformed mafic dike swarms of simple geometry cross-cut most shields. It has been suggested that their structural, pa Ieomagnetic, and chemical characteristics can provide estimates of variation in exposure-depth throughout a shield terrain [1,2,31. Preliminary work is reported below on the use of two structural parameters, dike dip and thickness, as possible depth-of-exposure indicators in the Central Superior Province. D i ke DIps The dike dip data for the Central Superior Province divide into geographic domains of like dip (Figure 1). Domains of non-vertical dip may originate either because the dikes were intruded in a near vertical attitude and subsequently tilted along with the host terrain or because the contemporaneous stress regime or inherited mechanical anisotropy favoured non-vertical intrusion. While intrusion along an inclined plane almost certainly explains some of the scatter in our data, it appears that the dominant cause of regionally inclined dike-dips in the Central Superior Province is post intrusion deformation.
    [Show full text]
  • The Geology of the Burke Quadrangle, Vermont
    THE GEOLOGY OF THE BURKE QUADRANGLE, VERMONT By BERTRAM G. WOODLAND off tC 200 STE STREET VERMONT GEOLOGICAL SURVEY CHARLES G. DOLL, State Geologist Published by VERMONT DEVELOPMENT DEIARTMENT MONTPELIER, VERMONT BULLETIN No. 28 1965 - Fiure 1. Fiontispie c Burke Mountain, Umpire \Iountain (left), and the northern spur of Kirby Mountain right) are resistant e-'se' of homteled Gilc \lount'&in fonuttion jj nuuite. View southeist\vards from near Marshall Swhool. TABLE OF CONTENTS PAGE ABSTRACT 9 INTRODUCTION ...................... 10 Location ........................ 10 Methods of study .................... 10 Acknowledgments .................... 12 Physiography ...................... 14 Settlement ....................... 17 Previous work ..................... 18 STRATIGRAPHY ...................... 19 General statement .................... 19 Thicknesses ..................... 19 Age of formations ................... 20 Sequence ....................... 20 Albee Formation ..................... 21 Amphibolite ...................... 22 Waits River Formation ................. 23 Impure limestone ................... 23 Pelitic rocks . . . . . . . . . . . . . . . . . . . . 24 Psammitic beds .................... 25 Amphibolite ...................... 27 Light-colored hornblende quartzose bands . . . . . . . 31 Meta-acid igneous rocks ................ 31 Gile Mountain Formation ................. 34 Quartzose phvllite ....................35 Pelitic rocks ...................... 39 Amphibolite . . . . . . . . . .
    [Show full text]